Metered dose inhalers provide a much-needed drug-delivery method that allows patients to aspirate medication rather than swallow a pill, or drink or inject medication. In some cases, as with medications that directly target the patient""s lungs, aspiration enables the medicine to reach the target area more quickly. In addition, aspiration is typically considered to be less painful than other drug-delivery methods.
Known metered dose inhalers typically include a pressurized cartridge containing an inhalant mixed with an aerosol propellant or carrier. The user places the inhaler""s mouthpiece in or over his mouth and/or nose and activates the inhaler, typically by mechanical opening of an atomizing valve. Activation of the inhaler thus releases a xe2x80x9cpuffxe2x80x9d of the inhalant-propellant mixture, which the user then aspirates through his mouth and/or nose.
The use of a pressurized cartridge can be problematic if the cartridge is ever breached. Because the contents of the cartridge are under pressure, a crack or break in the cartridge can lead to an unintended release of the inhalant, possibly without the user""s knowledge. This may increase costs to the patient, who may be forced to pay to replace lost medication, and can lead to unintentional dosing. This may be a significant concern as one use of inhalers is to allow patients to self-administer pain medications for which unintentional dosing may have serious consequences.
Furthermore, in some cases, it may be undesirable to maintain the medication in an aerosol carrier, or to administer medication with a chemical propellant. Many metered dose inhalers use chlorofluorocarbons (CFCs) as their propellant. The CFCs are inhaled by the patient, and then quickly eliminated by the body and released into the atmosphere. Due to environmental concerns raised by the use of CFCs, there have been recent governmental mandates to reduce and/or eliminate the use of CFCs in commercial products. Metered dose inhalers are one of the few products to have received a reprieve from these governmental mandates due to the lack of suitable replacements and the severity of the consequences if metered dose inhalers were to be removed from the market. Nevertheless, because a portion of each puff is propellant, the use of a propellant carrier may make dosage more inaccurate. For example, for medications requiring a very specific dosage, any variation in the ratio of propellant to medication may affect the efficacy of the medication.
Moreover, it has been shown that maximum effectiveness of pulmonary inhalation occurs over a rather limited range of droplet diameter sizes. These maximum effective sizes typically are in a range of 5 to 8 microns. Known metered dose inhalers may produce a large range of droplet sizes within a single puff, including droplets both above and below the ideal range. Those droplets that are too small are not retained by the lungs, and are instead exhaled out of the body. Likewise, those droplets that are too large are not absorbed by the lungs, and are also exhaled out of the body.
Finally, known inhalers have been limited to a single dosage. Typically, the only way to alter the dosage of a medication that is administered by an inhaler has been to either prescribe more than one xe2x80x9cpuffxe2x80x9d, or to prescribe a different-sized inhaler. Either of these situations may be undesirable, particularly if a patient wishes to decrease dosage during a treatment regime, for example, due to unwanted side effects from the medication. Thus, in some cases, it may be desirable to allow the patient to vary dosage (within a safe range). Alternatively, or additionally, it may be desirable to allow the doctor or pharmacist to alter the dosage during the course of treatment, for example, to provide a loading dose, or to ramp-up or ramp-down the amount of medication administered during the treatment regime.
The present invention provides a metered dose inhaler including an ejection mechanism with at least one chamber for containing a medicament. The ejection mechanism is configured to effect controlled ejection of medicament from the chamber. The inhaler further includes a controller configured to send an electronic signal to the ejection mechanism to direct ejection of medicament from the chamber, and configured to selectively alter dosage of the medicament by selected changes in such electronic signal.